Patients who have experienced ventricular fibrillation or who meet a risk profile for ventricular fibrillation are likely candidates for receiving an implantable medical device. An implantable medical device detects an episode of ventricular fibrillation, for example, and delivers one or more electrical shocks to the patient to stop the fibrillation and allow the heart to reestablish a normal sinus rhythm. In general, implantable medical devices deliver a shock at a first energy level upon detecting fibrillation and, if the fibrillation is not stopped, deliver additional shocks at increasing energy levels until the fibrillation is stopped or the programmed progression of shocks has been exhausted. For each shock, one or more defibrillation capacitors are charged to the desired energy level and then discharged to deliver the shock to the patient.
Implantable defibrillators often form part of implantable pacemakers. Implantable pacemaker-cardioverter-defibrillators (PCDs), for example, provide pacing, cardioversion and defibrillation functionality within a fully integrated implantable medical device (IMD). Implantable defibrillators can also form part of other types of IMDs.
One concern with implantable medical devices involves deformation of the defibrillation capacitors. Again, in order to deliver defibrillation shocks, one or more defibrillation capacitors are charged to a specific energy level and then discharged to deliver the energy to the patient as a defibrillation shock. Capacitor deformation, however, affects the ability to charge the defibrillation capacitors, and also affects the ability of the capacitor to effectively store charge. For example, capacitor deformation generally lengthens the amount of time that it takes to charge the capacitors and may reduce the ability of the capacitors to store the charge.
Capacitor reformation techniques have been developed to address the issue of capacitor deformation of defibrillation capacitors. In order to reform the defibrillation capacitors following extended periods of inactivity, a reformation process typically involves fully charging the defibrillation capacitors to repair the capacitors. Conventionally, reformation processes are programmed to occur within the implantable defibrillator at defined intervals, e.g., every three months or so. The reformation process repairs the defibrillation capacitors by rebuilding oxide layers, or the like. Accordingly, following reformation, the defibrillation capacitors should be capable of receiving charge more quickly, ensuring that defibrillation shocks can be delivered in a timely fashion. Unfortunately, however, each reformation process generally shortens the useful life of the defibrillation capacitors.